Power plants, such as combined power plants (for example, power plants including gas and steam turbines) can produce the base electric power that is supplied to an electric power grid.
With deregulation of the energy market, increased fuel prices and diffusion of renewable energies, combined power plants are more and more used to comply with peak power requests.
In order to comply with peak power requests, combined power plants can be asked to adapt their operation (in particular the power supplied to the grid) very fast, and should be able to operate with great flexibility. For example, when the energy required by the grid is low they should be able to reduce the power supplied to the grid up to zero and when the grid requires power again they should be able to provide it quickly. In some cases to provide tens of megawatt in seconds.
EP 2 056 421 discloses a method to connect a combined power plant with a gas turbine and a steam turbine to a grid. This method includes a first step where the gas turbine has full speed but does not supply any power to the grid. In addition the breaker is open. During this step the steam turbine loads up. In a second step the breaker is closed. During this step the steam turbine further loads up. In a third step the power plant energises the grid. Also during this step the steam turbine loads up. In a fourth step the power plant supplies power to the grid. During this step the steam turbine further loads up.
It is thus apparent that during the first through fourth steps the steam turbine does not supply any power to the grid. The steam turbine is in a transient, loading up operation. For this reason the method above could have some drawbacks.
When the steam turbine is in transient operation, it is not able to supply any power to the grid. The power plant cannot be able to satisfy a sudden power request from the grid. For example, in some cases sudden power requests from the grid can be as large as 50 MW/s or more.